1. Field of the Invention
The present invention relates to a carriage conveying system, and more particularly, to a carriage conveying system having a feeder cable arranged along a guide rail and a pickup coil provided for the carriage, which produces an induced electromotive force by alternating current applied to the feeder cable to supply electric power for the carriage to move the carriage along the guide rail.
2. Description of the Related Art
There are systems for transporting articles by a carriage moving along a guide rail to facilitate transportation of the articles in factories and warehouses. Normally, an operation motor drives the carriage. An electric driving force for the operation motors is supplied by applying a high frequency alternating current to a feeder cable (trolley cable for supplying electric power) that is arranged along the guide rail.
There are trolley type and non-contact type power supplying methods. In the trolley type method, the electric power is supplied by allowing contact between a collecting element provided for the carriage and the feeder cable. The non-contact method is described in, for example, Japanese Unexamined Patent Publication No. 6-153305. FIG. 15, herein, is representative of the trolley type device of Japanese Publication No. 6-153305. As shown in FIG. 15, a pickup device 53, which is provided for a carriage, moves along a guide rail 51, as shown in FIG. 15. A coil 55 of the pickup device 53 is arranged in the vicinity of a feeder cable 52, and the electric power is supplied by allowing the coil 55 to produce an induced electromotive force.
The trolley type method has problems such as wear of the collecting element, which necessitates maintenance, and dust and sparks. However, the non-contact method does not have these problems. From this point of view, the non-contact method is superior to the trolley type method, and has received more attention recently.
Conveyance of the carriage moving along the guide rail is controlled by instruction signals that are sent by a conveyance control device provided on the ground (or a ground station). The ground station performs the communication required for the conveyance of the carriage with the carriage moving along the guide rail. Such communication employs wireless devices that are provided for the ground station and the carriage. The carriage communicates with the ground station while moving, and the conveyance of the carriage is controlled by the instructions from the ground station.
In this communication method, the guide rail is installed over a large area. Thus, the wireless devices of the ground station must be arranged at optimal locations to assure the communication regardless of the position of the carriage that is moving. This increases the workload and time required for installing the communication cable that connects the wireless devices and the ground station. Furthermore, the workload and time required for choosing the locations for installing the wireless devices of the ground station are also increased to assure communication with the carriage.
Therefore, a communication cable connected to the ground station may be arranged along the guide rail extending parallel with the feeder cable to enable communication between the carriage and the ground station via the communication cable. However, in such cases, installation of the communication cable along the guide rail increases the workload and time required for the wiring of the guide rail. Furthermore, since the collecting element contacts the communication cable, the communication cable and the collecting element become worn. The wear may cause faulty communication. To avoid such problems, the communication cable and the collecting element must be changed periodically. In addition, a larger guide rail is required for installing the communication cable along the rail.